This invention relates to devices for sensing pressure differentials, and more particularly to a device for sensing relative pressure differentials in a temperature variable environment. This invention further relates to a structure for a temperature compensated pressure differential sensing device adapted for easy calibration and adapted for easy testing of the operability thereof.
There are many situations wherein it is desirable to monitor the status of a pressurized device. One such situation relates to helicopters, and more particularly to helicopter blades which are hollow and filled with a pressurized gas. A loss of or decrease in the pressurization of the blade indicates a defect in the structural integrity of the blade. Defects may be caused by traumatic damage, such as bullet holes, or may be caused by other structural failure, such as fatigue cracks. It is important for the pilot of a helicopter to know immediately if depressurization has occurred, so that he may take appropriate action including landing the helicopter promptly for repairs.
The helicopter blade environment poses problems to a successful pressure monitoring device. A helicopter operates at varying altitudes and consequent wide ranges of temperatures which cause the pressurization of the blade to change. Further, there are vibration and stress loads present in this environment. Also, there is a need for prompt and accurate information concerning pressurization of the blades, and fail-safe operation of the indicator itself is preferable. In addition, such a device should be capable of fast and simple testing of its operability, and provisions for such testing must not in and of themselves be a source of failure.
Prior art helicopter blade pressure monitoring devices made no attempt to provide an indication of depressurization during flight. These prior art devices were primarily useful for measuring gross deviations in pressure, and had to be read prior to and after flights, and slow depressurization caused by a fatigue crack might not become apparent on the indicator for a substantial period of time.